As semiconductor device dimensions decrease, the need to perform lithography at shorter wavelengths becomes more critical. One method of simulating the results achievable by direct application of short wavelengths, is to apply longer wavelengths through refractive liquid. Accurate determination of the refractive index of liquids to be applied in said simulated shorter wavelength lithography then becomes critical.
A well known technique for determining the refractive index of a material is to provide a triangular shaped prism of the material, mount it to a front of a rotatable stage, provide a beam of electromagnetic radiation which is directed to impinge upon one side thereof, and further provide a pivot mounted detector which is positionable to intercept the beam of electromagnetic radiation which exits said triangular shaped prism. This can be visualized in elevation where the rotatable stage is pivotally mounted to a horizontally projected axile means about which said rotatable stage can be caused to rotate, (eg. a projecting rod), which extends from a vertically oriented support. The source of electromagnetic radiation can be envisioned as fixedly mounted to the right (left) of said rotatably mounted stage with the detector mounted to the left (right) via an arm which is pivotally mounted at the location of the horizontally projected means about which said rotatable stage can be caused to rotate, to which is pivotally mounted at said rotatable stage. Note, the described orientation of the system is exemplary only, and the entire system can be rotated to orient the horizontally projected axile means about which said rotatable stage rotates vertically, so that the front of the stage faces vertically, or for that matter, oriented in any functional direction. Of course it is assumed that the Source of electromagnetic radiation and stage front and detector stay relatively in the same orientation with respect to said projected projected axile means during any such rotation.
Known Article references are:    “Refractive Index and Dispersion of Distilled Water for Visible Radiation, at Temperatures 0 to 60° Centigrade”, Tilton et al., NIST, (1938).    “Revised Formulation for the Refractive Index of Water and Steam as a Function of Wavelength, Temperature ad Density”, Harvey et al., J. Phys. Chem. Data, Vol. 27, No. 4 (1998).    “Measurement of the Refractive Index of a Prism by a Critical Angle Method”, Talim, Optica Acta, Vol. 25, No. 2 (1978).    “Refractive-index Measurement of Bulk Materials: Prism Coupling Method”, Onodera et al., Applied Optics, Vol. 22, No. 8, (1983).    “Refractive Index of Liquid Solutions at Low Temperatures: An Accurate Measurement”, Grange et al. Applied Optics, Vol. 15, No. 4, (1976).    “Alternatives to the Minimum Deviation Method for Refractive Index Measurement”, Dougal, Am. J. Phys. 54(4) (1996).    “A Simple, Accurate Alternative to the Minimum Deviation Method of Determining the Refractive Index of Liquids”, Chandra et al. Am. J. Phys. 51(2), (1983).    “Absolute Refractive Indicies and Thermal Coefficients of Fused Silica and Calcium Fluoride Near 193 NM”, Gupta et al., Applied Optics, Vol. 37, No. 25, (1998).    “Absolute Refractive Indicies and Thermal Coefficients of CaF2, SrF2, BaF2, and LiF Near 157 NM”, Applied Optics, Vol. 41, No. 13, (2002).    “Measurement of the Refractive Index and ThermopOptic Coefficient of Water Near 193 NM”, Proc. SPIE, Optical Microlithography XVI, (2003).    “Immersion Fluid Refractive Indicies Using Prism Minimum Deviation Techniques”, French et al., Proc. SPIE, Vol. 5377, Op. Microlithography XVII, (2004).    “Immersion Fluids for Lithography: Refractive Index Measurement using Prism Minimum Deviation Techniques”, Synowicki et al., Semiconductor Fabtech, 22nd Edition, Henely Publishing Ltd., London, UK.    “Refractometry by Minimum Deviation: Accuracy Analysis”, Tentori et al., Op. Engineering, Vol. 29, No. 2, February (1980).    “Prism”, Wolfram Science World, found at Website http://scienceworld.wolfram.com/physics/Prism.html.
A Search of patents which describe apparatus and methodology which can be applied to a similar end as taught in this Application has provided:                U.S. Pat. No. 4,756,618 to Spry;        U.S. Pat. No. 3,797,940 to King;        U.S. Pat. No. 3,450,476 to Rando;        U.S. Pat. No. 3,090,222 to Akabosch et al.;        U.S. Pat. No. 2,649,014 to Johnsen;        U.S. Pat. No. 2,649,013 to Schnelle;        U.S. Pat. No. 5,696,580 to Kubo et al.;        U.S. Pat. No. 4,381,895 to Hughes et al.;        U.S. Pat. No. 6,549,276 to Longtin;        U.S. Pat. No. 4,286,873 to Carson;        U.S. Pat. No. 4,284,352 to Carson et al.;        U.S. Pat. No. 3,449,051 to Levitt;        U.S. Pat. No. 2,972,926 to Goldberg et al.;        U.S. Pat. No. 2,413,208 to Barnes.        
Need remains for apparatus and methodology of its application in the area of determining optical properties of fluids and in particular, liquids.